How to process command with && (and) as parameter?

Question

In my script I want to proceed first argument as necessary file name and all other arguments as shell commands separated by && (and operator).

echo "${@:2}"

But Bash cuts all commands except first one.

How to fix it?

#!/usr/bin/env bash
while inotifywait -q -e close_write -e delete $1; do "${@:2}"; du app; done;

./watch . g++ app.cpp -o app && time ./app && du app

Answer 1

Alex, I get the jest of what you are attempting to do with inotifywait, but when I attempted it, it would just hang and do nothing as the files were static at the point it was called. Looking at what you are attempting to accomplish. (build, run, measure disk usage of app) it may be easier to just script it instead of putting inotifywait in the middle of it.

While this is just a basic hack at getting the output you wanted. The script below will take the source file as the first argument (app.cpp by default if no name given) and will compile the code using the name before .cpp as the g++ output file name. It is a simple attempt to get the information you were looking for:

#!/bin/bash

src=${1:-app.cpp}   ## set the source and output (exe) names
out=${src%.cpp}

printf "\n compiling 'g++ %s -o %s'\n\n" $src $out

[ -f $out ] && rm $out      ## remove existing exe before builinding

g++ $src -o $out            ## build new exe

[ -f $out ] || {            ## validate new exe created
    printf "error: compilation failed. exiting script.\n\n"
    printf "usage:   %s source.cpp (default: app.cpp)\n\n"
    exit 1
}

[ -e $out ] || {            ## validate it is executable
    printf "error: file produced from compilation is not executable.\n"
    exit 1
}

time ./$out 2>&1                        ## compute elapsed time
exesz=$(du -h $out | awk '{print $1}')  ## store disk usage (removing name)

## print results
printf "\n Source file:  %s\n" "$src"
printf " output file:  %s\n" "$out"
printf " size of exe:  %s bytes\n\n" "$exesz"

exit 0

Example Output

$ ./watch.sh

 compiling 'g++ app.cpp -o app'

Code Running
and being timed.

real    0m0.004s
user    0m0.001s
sys     0m0.002s

 Source file:  app.cpp
 output file:  app
 size of exe:  16K bytes

The test code I used was a simple cout:

#include <iostream>

using namespace std;

int main (void) {
    cout << "Code Running" << endl << "and being timed." << endl;
    return 0;
}

Incorporating iowaitnotify

Understanding better what you are attempting to accomplish, below is an addition (without all the validation checks) that will watch your source file and recompile on any change. It also avoids the use of eval. There are several ways to accomplish this, this being one. You can add the validation checks from the script above if you desire:

#!/bin/bash

bldcmd=( ${@:2} )   ## array for build command

while inotifywait -q -e close_write -e delete $1; do 
    echo -e "\ncompiling:  ${bldcmd[@]}"
    # eval "${@:2}"
    ${bldcmd[@]}
    time ./app
    printf "\n app size: %s\n" $(du -h app | awk '{print $1}')
done

Output

$ ./watch . g++ app.cpp -o app
./ CLOSE_WRITE,CLOSE app.cpp

compiling:  g++ app.cpp -o app

Code Running (ver. 6)
and being timed.

real    0m0.003s
user    0m0.001s
sys     0m0.002s

 app size: 16K

Answer 2

I'm not sure I've read the question correctly, but I think you're asking how to watch a pipeline, i.e. repeatedly run g++ app.cpp -o app && time ./app && du app. If that's what you need to do, you must quote && so it's not interpreted by your (top-level) shell, but instead by the shell that watch invokes:

watch g++ app.cpp -o app '&&' time ./app '&&' du app

You could of course use backslash escaping (\&\& instead of '&&') if you prefer.

Answer 3

Solution is eval command .